Patch clamp techniques are utilized in electrophysiology to enable the study of single or multiple ion channels in biological cells and other tissues. In a traditional patch clamp technique, a cell is provided in a bath solution, and a glass micropipette having an inside diameter of about 1 μm is pressed against the surface of the membrane of a cell. The portion of the membrane surface of the cell covered by the micropipette is known as the “patch.” A small amount of suction is applied through the micropipette to form a high-resistance seal between the cell membrane and the micropipette. The micropipette is filled with an electrolyte, a silver chloride electrode (wire) is inserted into the electrolyte and a grounded electrode may be placed in contact with the bath, thereby enabling the measurement of electrical current resulting from ion flow through the ion channel associated with the patch. The high resistance of the seal formed between the cell membrane and the micropipette functions to electrically isolate the current being measured and minimize the signal-to-noise ratio of the measurement being recorded. It is typically desired that the resistance of the seal be as high as 1 GΩ or higher; such seals are termed “giga-ohm seals” or “gigaseals.”
Patch clamps employing micropipettes increasingly are being replaced by planar patch clamp devices. Planar patch clamp devices are generally provided in the form of microfabricated substrates. Planar patch clamp devices include planar substrates with apertures of 1-2 μm in diameter that function as the tips of micropipettes. Suction and/or an electric field are applied so as to position a cell on the aperture, and the high-resistance seal is formed between the cell membrane and the substrate in the vicinity of the aperture. The substrate may serve as a partition between respective fluid compartments located above and below the substrate, with the aperture fluidly interconnecting the two fluid compartments. A measurement electrode may be placed in the fluid compartment in which the cell resides, and a grounded electrode may be placed in the other fluid compartment.
Planar patch clamp devices are amenable to high-throughput assaying systems and cooperation with microfluidic components. The substrates have typically been composed of quartz or glass. Some commercially available glass substrates have proprietary coatings designed to enhance the ability to form giga-ohm seals (i.e., increase the success rate in forming giga-ohm seals). Alternative substrate materials have also been proposed, such as silicon as disclosed in U.S. Pat. No. 7,387,715. This patent describes a number of planar structures for positioning cells and performing electrical and/or optical analyses related to the presence and activity of ion channels, but does not teach any particular combination of low-cost materials and configurations that would be optimal for the formation of high-quality giga-ohm seals.
High seal resistance between the living cell and the substrate of a planar patch clamp device is highly desirable for achieving high-quality recordings of ion channel activities. Therefore, there is an ongoing need for providing planar patch clamp devices capable of achieving high seal resistance at a reasonable cost. There is also a need for providing planar patch clamp devices capable of reliably forming high-quality giga-ohm seals with high success rates.